Obesity is one of the greatest health challenges currently facing the world. The rising prevalence of obesity among children and adolescents is of particular concern and suggests worsening trends for the future. Currently, the only truly effective long-term exogenous treatment for obesity is bariatric surgery, the long-term benefits of which may actually involve gut hormones such as PYY, the focus of this proposal. While drug treatment is often prescribed for the management of obesity, average placebo-subtracted weight losses are less than 5% with currently licensed antiobesity drugs. As a consequence, novel antiobesity drugs with increased efficacy and safety are currently being sought. One area of great interest focuses on select endogenous peptides as potential antiobesity therapeutics due to their appetite suppressing effects. Currently available administration routes for peptides (primarily injection) have limited their suitability in a clinical setting however. The aim of this project is to demonstrate an effective oral delivery route and suitable in vivo agonism for the gut hormone PYY3-36, which has been established as having appetite suppressing properties. In addition, understanding the effects of peripheral PYY3-36 administration and the interactions with other important gut hormones such as GLP-1 for instance, remains in question. An orally active PYY3-36 that can be administered without stress to the animal, a major issue to date in peripheral studies, would be of significant benefit to the field. The three specific aims of this proposal are clearly designed towards our production and understanding of an orally active PYY3-36, ultimately suitable for peripheral in vivo investigations beyond the animal models proposed here. Aim 1 will produce four new conjugates based on a rational design. Aim 2 will screen such conjugates for receptor specificity and potency and aim 3 will provide insight into the metabolic effects in vivo. C1) Aim 1. Synthesize four vitamin B12-PYY3-36 conjugates (and one scrambled PYY3-36 control) for in vitro screening. Using rational design a series of B12-PYY3-36 conjugates will be chemically synthesized and characterized. C2) Aim 2. Screen conjugates for Y1 versus Y2 Receptor selectivity and agonistic activity. Weight loss effects are believed to stem from activation of Y2-R, with the opposite effects triggered by Y1 activation. Conjugates with selectivity for Y2-R over Y1-R with equipotent (compared to PYY3-36) or similarly low nanomolar potency for Y2-R will be screened out for in vivo investigations C3) Aim 3. Conduct biological and in vivo uptake studies with successfully screened conjugate. We will attempt to show that the B12-PYY3-36 conjugate is in a bioavailable form and will result in an anorectic effect similar to that of subcutaneously administered free PYY3-36. Biochemical effects triggered by oral administration in addition to feeding will be Lee adiposity index, and c-Fos. Secondary outcomes include PYY, insulin and glucose from serum samples.